Effect of Captive Stores on Internal Weapons Bay Floor Pressure Distributions

T HE new generation of stores to be used on the F-22 and joint strike fighter (JSF) are designed as efficiently packaged, small, highly lethal minimissiles. Because of their lighter weights and smaller moments of inertia, these small smart bombs (SSB) are more easily perturbed by flowfield effects than heavier stores carried externally in older aircraft. This can result in unsafe separations and targeting inaccuracies. For this reason, the majority of studies on internal weapons bays are focused on the stores’ separation problem. A recent investigation on wind-tunnel and flight-test comparisons is given by Grove et al. [1]. However, aircraft weapons bays exposed to high subsonic or supersonic flows are subjected to an intense aeroacoustic field inside the bay. TheM219 cavity [2] is often used as a test case for computational fluid dynamic (CFD) and wind-tunnel test comparisons. For a length-to-depth ratio of 5, Lee et al. [3] measured the frequency of the pressure oscillations on the cavity floor. The frequency for the first three modes at a Mach number of M 1:11when scaled to a typical weapons bay of 13 ft length gives values for f1 23 Hz, f2 56 Hz, and f3 90 Hz, respectively. The large pressure oscillations at these low frequencies can lead to structural fatigue of theweapons bay walls and damages to the stores and electronic equipment. Data on the effect of small stores typical of the dimensions of the SSB on the unsteady pressure inside aweapons bay are lacking. This paper presents some preliminary results on the floor pressure measurements of a generic weapons bay for small stores at forwardand aft-release positions. The perturbations introduced by the stores are found to cause significant changes in the acoustic wave intensities inside the M219 cavity.